Two research projects are proposed: 1) Evaluation of mechanically generated reflexes controlling the motor act of breathing - This study is an outgrowth of current research showing that the larynx is a prime respiratory organ regulating the rhythm of breathing in unanesthetized cats. Cats will be studied before and after intra-thoracic vagotomy and thoracic dorsal rhizotomy. Use of the latter neurotomy is based on recent evidence showing that intercostal muscle afferents influence bulbo-pontine neurons setting the respiratory rhythm. The duration of the respiratory phase and laryngeal resistance will be measured in sleeping, awake and exercising cats. 2) Exploration of neuronal mechanisms responsible for termination of inspiration - A variety of afferent inputs, plus a descending influence from the pneumotaxic area, act to arrest medullary inspiratory activity. All probably act through a common group of "switch neurons", perhaps located in the caudal pons. The location and behavior of these postulated neurons will be investigated by microelectrodes.